The present invention relates to a procedure by which the controlling of on/off type switches of a radio unit or the RF part of a radio telephone can be arranged without having to draw separate control lines from the logic unit of the telephone to the switches.
The radio part of any modern radio telephone comprises a plurality of controlled switches with which a given electrical circuit can be switched to be active or off, or its parameters can be changed. These switches are two-position switches, normally bipolar transistors or FETs, and they control, for instance, switchable filters or regulators of the transmitter. These switches are in turn controlled by a logic unit (processor) of the radio telephone, from which an individual control line, i.e. a lead, extends to each switch and over which a logic "1" or "0", i.e. voltage "high" or "low", is carried to the base of the transistor or FET serving as the switch. The logic unit also controls frequency synthesizers by which the local oscillator frequencies of the transmitter and receiver are produced. As is known in the art, a frequency synthesizer comprises a phase-locked loop (PLL) with a phase comparator, a voltage controlled oscillator (VCO), and a programmable divider, dividing the initial frequency of the VCO prior to its being carried to the second input of the phase comparator. The initial frequency of the loop is determined by the above mentioned programmable divider. The logic unit sets the frequency synthesizer to the desired channel by changing, over a control line, the division number of the divider to be consistent with the desired channel. Usually there are three control lines: by one of these lines the division number is supplied in binary serial form to the register of the phase-locked loop; by a second line a timing signal (clock pulse) is sent, and by the third line, an enable pulse, which on arrival in the phase-locked loop causes the loop division number, supplied to the registers, to be transmitted from the registers of the loop circuit to become the contents of counters.
Also such frequency synthesizer components, implemented using one integrated circuit, are known in the art in which the control word used for channel change sets certain connecting pins of the circuit to a "one" or "zero" state. From these pins, control may be derived for external controlled switches. In these circuits, the decoding logic required for implementing the function is integrated into the PLL circuit.
The switch control line methods of the prior art are encumbered by some drawbacks. As mentioned above, each controlled switch in the radio unit requires an individual control line from a processor, although in certain instances one control line is able to control a number of switches. Therefore, the greater the number of controlled switches in the circuit, the more control lines which are needed. This is an inconvenience when designing a circuit board. If the switches to be controlled and the processor are mounted on separate circuit boards, a multiple pin connector is needed to transfer the control signals from one board to another. If connecting pins of the PLL circuit are utilized in the control, the number of pins must be increased, and this leads to greater physical bulk. This is a nuisance in developing telephones of smaller size. Furthermore, it may be noted that PLL components of this type that are appropriate for portable telephone applications, are hard to find.